In this section, we discuss several aspects of related work, including background and conventional technologies.
Clays
Clay is an aluminosilicate, which has a layered sheet-like structure with silica tetrahedral bonded to alumina octahedral in different ratios through Van der Waal's forces. Types of clay with a 2:1 ratio of tetrahedral to octahedral are known as smectite clays. A common type of smectite clay is Montmorillonite (MMT).
Clays are common ingredients in pharmaceutical products. Clay minerals are naturally occurring inorganic cationic exchangers and so they can undergo ion exchange with basic drugs in solution. In addition to ion-exchange, organic molecules can bond to clays via physical adsorption and ion-dipole interactions of acidic and non-ionized molecules. For example. Wai and Banker demonstrated the loading of alkaloids in montmorillonite clay.
Medicinal and therapeutic applications of various clays and their products have long been used for the treatment of skin ailments. Montmorillonite (MMT) is one of the most widely used medicinal clays. Studies have shown that MMT is non-toxic and thus has no side effects. Montmorillonite and its products have a broad spectrum of applications in medicine for cleansing and protection of skin, antibacterial activity and blood clotting capabilities. Clay can also accelerate healing in simple wounds.
MMT has also been used in the delivery of vitamins such as thiamine hydrochloride (Vitamin B1; VB1) and pyridoxine hydrochloride (Vitamin B6; VB6) to the intestinal environment. The controlled release of VB1/VB6 was observed.
Another major advantage of using clays to deliver drugs is the very low risk of ‘dose dumping’. Dose dumping is an unexpected sudden release of the entire dose, which may cause severe or even lethal side effects because of the narrow therapeutic window of high potency drugs. Common topical medical dressings such as gauze, membranes and textiles can be subjected to dose dumping easily due to external forces such as temperature change, pH change, and enzyme activity. Thus, a material of high chemical and mechanical resistance is required to develop a safe, high potency opioid transdermal drug delivery vehicle. Clays are the most optimum materials for storage and delivery systems for drugs such as analgesics because of the mechanical and chemical stability of clay. For example, Fentanyl has been loaded into a metakaolin clay, which provided a mechanically strong sustained drug release medium.
Typically, clay particles are dispersed in aqueous drug solutions, dispersions are allowed to equilibrate for a suitable time, and finally solid particulates are recovered and dried. Clay in the particulate form (powders) are not suitable for use in preparing topical wound dressing or for transdermal application of drugs because these methods require a continuous film so that drugs can diffuse without interruption from the dressing. In the case of clay particles there does not exist a continuous path for drugs to diffuse from the clay particles to wound or skin surface. Clays in the form of thin sheets are preferable for topical wound dressing and transdermal drug delivery applications.
Clay sheets made using polymer binders which are commonly known as ‘polymer-clay composites’ are available in the market. In these polymer-clay composites, the polymers act as a medium to disperse clay particles and to provide mechanical stability to the polymer-clay composite sheets. The clay nanocomposite of various polymeric materials such as polystyrene, nylon-6, polyaniline, polymethyl methacrylate (PMMA), polyurethane, polyethylene, poly (styrene-co-acrylonitrile), polyaniline, polypyrrole, polysulfone, polyacrylates, polyimide and epoxy have been investigated for a variety of applications.
The initial question that arose was how to create a clay film that does not fall apart and does not make use of significantly large polymers. It is preferable to have clay sheets without any polymer additives in certain applications where polymer additives can hinder or reduce the permeation of moisture, or chemicals or drugs though the clay sheets. It is also preferable to have a continuous sheet clay uninterrupted by the polymer matrix. In this way special properties of clay particles such as adsorption, permeability, high temperature stability, ion-exchange property, hemostasis property, and wound healing property can be fully utilized without being disturbed by the properties of polymer additives.
Antimicrobial Burn Wound Dressing
Antimicrobial silver-nylon dressing product known in the prior art prevents infection at a surgical site, enhances negative pressure therapy and help treat burns and wounds. These dressings have a permanently plated metallic surface. They continuously deliver a flow of silver ions into the wound, can be used for up to 7 days, do not increase the number of contaminating microbes before sterilization and do not stain.
Another prior art product contains two layers of silver-coated polyethylene mesh, enclosing a layer of rayon and polyester. The silver is put on the polyethylene mesh in a vapor deposition process. This process leads to the formation of nanocrystals of the metallic silver which help fight against the various gram positive and negative bacteria. This product is mainly used as a barrier layer for burns and donor sites. The difference between these products and this disclosure is that these products release silver into the wounded area to tight the microbes. The silver ions in this disclosure are contained within the clay film.
Transdermal Drug Delivery
Burns are among the most painful and debilitating battlefield wounds faced by the US warfighter. Burn wounds turn deadly when infection sets in. Since military operations began in Iraq in March 2003, hundreds of US military personnel have sustained burn injuries from explosions and other implements of war such as IED's. Not only is acute burn injury pain a source of immense suffering, but it has been linked to debilitating chronic pain and stress-related disorders. Severe pain is felt during acute treatment and rehabilitation, especially during dressing changes, debridement's, and skin grafting, and continues through long-term follow up. The backbone of burn analgesia is opioid therapy, typically administered via oral or parenteral routes. The use of opioid medications in burn patients is complicated by the side effects such as tolerance, hyperalgesia, hemodynamic instability, respiratory depression, and dependence. Therefore, beside the systemic administration of analgesics, attempts have been made to control the pain locally using topical analgesics which has shown encouraging results. Such topical dressings can be used to protect the burn wound from infection and thereby aid in wound healing if an antimicrobial property can be imparted onto them.
Treatment for reducing the pain involves the usage of common and opioid analgesics, nonsteroidal anti-inflammatory drugs (NSAIDs) and adjuvant analgesics. Pharmacologically, it is known that the main mechanism of action of analgesics is to act at specific sites located in the CNS and periphery. This observation led topical administration of pain reliever drugs such as NSAID's, local anesthetics, capsaicin, tricyclic antidepressants, ketamine, clonidine, opioids, and cannabinoids. For example, fentanyl transdermal patches are used in chronic pain such as cancer pain or in the post-operative setting. The topical application of these drugs allows high concentrations in peripheral effector sites. Thus, undesirable side effects are less likely to occur compared to delivering these drugs systemically. Even though opioid drugs are applied locally on the skin, the main analgesic action of opioids occurs only in the spinal cord. This will require the drug to be absorbed into the blood and travel from the skin surface to the spinal cord.
Local anesthetic creams have been used in burn wound dressings. For example, Lidocaine prilocalne cream has been used as a topical anesthetic by physicians performing plastic surgery and in patients with face burn injury. Topical application of loperamide also reduced the pain in full-thickness burn wounds by acting on the peripheral nociceptors. Therefore, a combination of local anesthetics such as lidocaine and opioid drugs such as fentanyl may be incorporated in to the clay sheets and can be used in transdermal pain medication.
Separation Membrane
The United States must develop and deploy clean, affordable, domestic energy sources as quickly as possible to achieve energy security and independence. Batteries power everything from tools to cars to remote controls and have a major role in our daily lives. There is an increasing interest in the energy efficient production of Dimethyl Carbonate (DMC) that will support a growing market for hybrids and electric vehicles, and significantly reduce our dependence on foreign oil as well as correspondingly reduce greenhouse gas emissions.
Dimethyl carbonate is used as a substitute for toxic products such as phosgene as well as traditional methylation agents. Other applications include as a solvent for coatings, an octane booster in petrol, and as a component of diesel. In the last decade DMC has shown immense promise as an electrolyte solvent for lithium battery applications due to its inherent safety and robustness. Despite the enormous promise of its industrial use, this chemical is currently entirely imported from China and Japan. Recently, South Korea has entered into the global DMC production foray. Other global chemical industries include EniChem (Italy), Bayer (Germany) and Catalytic Distillation Technologies (Netherlands), and to a certain extent, BASF (Germany).
Carbon dioxide conversion to DMC is a very challenging and sensitive reaction, because of the high Carbon dioxide activation energy required to convert Carbon dioxide and methanol. Most reports concentrate on gas phase reaction and conversion of carbon dioxide to DMC with 3.5% yield.
One of the critical problems of catalytic direct synthesis of DMC is the co-generation of water, which causes hydrolysis of the DMC formed during the reaction. It is thus important to remove the water generated during the reaction.